1. Field of the Invention
The invention relates in general to high speed communications, and in particular, to a voltage controlled oscillator utilized in high speed communications.
2. Description of the Related Art
Requirement for transmission of high-speed data has increased in recent years, for applications such as computers, telecommunication devices, RF IC technologies, and high-frequency clocks. High-speed voltage controlled oscillators and frequency dividers are essential building blocks commonly employed in computer and telecommunication applications for functions such as frequency synthesis, up-conversion and down-conversion. For example, a prescaler implemented by a frequency divider is one of the important components in a phase-locked loop (PLL) (FIG. 1), widely used as frequency synthesizers in a radio transceiver. Static or dynamic digital frequency dividers are commonly used in RF/microwave PLLs. They have simple structures, large bandwidths, and good robustness over process variations. However, as radio operation frequencies increase beyond the low GHz range, power consumption of digital dividers becomes a problem. Namely, it becomes increasingly difficult for digital frequency dividers to meet power requirements, with the problem particularly challenging for low-powered mobile applications. Furthermore, due to large power dissipation, high-speed digital dividers may also result in considerable noise degradation.
Voltage controlled oscillators typically utilize inductors and capacitor banks to form a resonance network, and generate high-frequency oscillation signals. Generally, the inductors and capacitor banks occupy large circuit areas when compared with other circuits in an IC, resulting in requirement for larger IC circuit dimensions, thus raising manufacturing costs.
Thus, a voltage controlled oscillator and frequency divider with better power efficiency and a more compact circuit dimension is needed.